Epsom Salt for Mg supplement

[JRechcygl]

Why is magnesium chloride preferred over epsom salts as a Mg supplement? Is it because the ionic balance? The way I look at it most commercial Mg supplements are MgSO4 with NaCl, if the ionic balance is the problem, wouldn't the CaCl2 supplement I'm using keep it in line? Or if like the commercial ones couldn't I throw in a pinch of uniodized salt?

[reef_doug]

Epson salt alone will have too much residual sulfate after awhile.
Randy has two recipes, one for maintaining and one for raising/correction. Both use a combination of MagFlake & Epson Salt:

Maintenance:
An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System
http://reefkeeping.com/issues/2006-02/rhf/index.php

Raising Mg (I use recipe version #3 towards the very bottom)
Do-It-Yourself Magnesium Supplements for the Reef Aquarium
http://reefkeeping.com/issues/2006-07/rhf/index.php

If you want an over-the-counter supplement, then Kent Tech-M is a good choice.

[Randy Holmes-Farley]

Yes, ionic balance. The mixture is more preferred over either one by itself as well. I show that here:

Do-It-Yourself Magnesium Supplements for the Reef Aquarium
http://reefkeeping.com/issues/2006-07/rhf/index.php


Calcium chloride helps keep it in line, but not enough. I show that here, and that is why my "improved" two part system with both mag chloride and mag sulfate is better than the one with mag sulfate alone:

An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System
http://reefkeeping.com/issues/2006-02/rhf/index.php

Specifically, compare table 2 to table 3. Using mag sulfate alone leads to sulfate rising from 2710 to 3840 ppm after one year (with no water changes). Using the right ratio of both leads to no significant sulfate change.


I show here how water changes impact the sulfate rise:

Water Changes in Reef Aquaria
http://reefkeeping.com/issues/2005-10/rhf/index.php

from it;

http://reefkeeping.com/issues/2005-10/rhf/images/Figure25sm.GIF

Figure 25. Sulfate concentration as a function of time when performing daily water changes equivalent to 0% (no changes), 7.5%, 15% and 30% of the total volume each month (in other words, 0%, 0.25%, 0.5% and 1% per day). In this example, sulfate starts at a natural level of 2710 ppm, and the model assumes usage of a moderate amount of calcium chloride and sodium bicarbonate to maintain calcium and alkalinity, and Epsom salts (magnesium sulfate) to maintain magnesium.

[Randy Holmes-Farley]

Adding salt (NaCl) does not have enough impact until you add so much salt that what you have is a salt mix (since that is ionically balanced), unless you add so much that you are making a salt mix itself.

Seachem takes this approach with their additive, but IMO it is a flawed method and cannot provide ionic balance.

[JRechcygl]

That's what I was thinking, on the tank I was planning on expirementing this on gets regular 10-20% H2O changes either weekly or bi weekly(I have kids and not enough time!) so I'm not too concerned about too much sulfate, but I was also planning once things slow down on doing a complete 2 part mix for the tank. And you hit the nail on the head Randy with the Seachem, thats one of the supplements I was thinking about. Thanks for your help

[Randy Holmes-Farley]

You're welcome.

Happy Reefing. :)

[Qdoggie]

Any of you had problems with epsom salts not mixing all the way as described in Farley's article?

[Mike O'Brien]

Only when mixing it with MgCl. Other than that it dissolves without a problem.

[BigJay]

I read both of Randy's articles and I'm confused. I am using epsom salts from the pharmacy, and a big gallon tub of mag chloride from BRS.

To raise magnesium in my water change make-up water, do I use the 5 cups MgCl + 3 cups MgSO4, or do I use the 7 1/4 cup MgCl + 3/4 cup MgSO4 formula?

Thanks!

[Mike O'Brien]

There are two different recipes. The one that goes along with the DIY two part is balanced to the two part, the 3:5. The other recipe is a stand alone supplement.